Bariatric surgery, including RYGB is also associated with medical and nutritional complications. This will be a natural consequence of the fact that the food bypasses virtually the entire ventricle and 100-150 cm of the upper part of the small intestine after a RYGB. Therefore, problems with uptake of for example B12, iron, folate, thiamin, fat-soluble vitamins (Vitamins A, D, E and K) copper, zinc and selenium are expected. In the light of this, it is decided that all RYGB operated patients must take vitamin B12, iron and vitamin D substitution. In spite of this, many develop various nutritional problems after RYGB. In addition to these nutritional complications are complications such as hypoglycaemia and gallstone attacks after RYGB.